Many polymeric substrates are hydrophobic and inert owing to their non-polar nature. For example, polymers that are olefinic can show high hydrophobicity. Some applications may require that the surfaces of polymeric substrates instead be hydrophilic. For example, surfaces used in microfluidics, surfaces of biological and medical devices, sensors, or other devices may need to be hydrophilic. In another example, tissue growth is encouraged on hydrophilic surfaces, which may or may not show biorecognizable moieties (such as RGD peptides, proteins, or other molecules or cells). In yet another example, battery separators made of olefins need to be wettable to efficiently fill the battery space with electrolyte.
In other embodiments it may be desirable to modify the surfaces of inert fibers with functional chemistry. For example, the surface of a polyolefin or other inert fibers may be treated with a flame retardant sheath that enables production of high mechanical strength fibers (i.e., no flame retardants in the core of the fiber) while the surface offers inhibitory action towards propagating flame. This could be desirable in cheap fabrics made of inexpensive polyolefins. Depending on the flame retardant or anchor used, this may render the fiber hydrophilic or hydrophobic.
It may also be desirable to have synthetic low cost fibers be surface modified to provide a better hand (“feel”), or the appearance of a natural fiber surface while the core is of a synthetic fiber. Hand is the quality of a fabric assessed by the reaction obtained from the sense of touch. Surface modification may be necessary to impart, for example, a certain hand of cotton to synthetic fibers. This could be accomplished by modifying the surfaces of synthetic fiber surfaces using a cellulosic derivative, which may render the fiber surfaces hydrophilic.
Surface modification could also be used to impart a superior hydrophobicity to synthetic polymer surfaces. Melt additives that segregate to surfaces and surface coatings that bind to melt additives at interfaces may be desired.
In other embodiments where it is desired to have a surface polymer or material of another type be hydrophilic, such as rendering a surface to be able to attract and attach itself to protein, the surface can be modified to exhibit such properties.
Rendering surfaces hydrophilic or hydrophobic or otherwise modifying the surface of a material can present challenges during manufacturing. Previous methods have applied a topical coating or some other material after the article is made, but this may be removed during, for example, use, wearing, or washing. New durable methods to modify the surface of a material are needed in the art.